DE69924586T2 - Magnetoresistance effect element - Google Patents

Description

The The invention relates to a magnetoresistance effect element comprising a has high magnetic sensitivity and as a magnetic sensor for detecting weak magnetic fields can be used.

One compact magnetic sensor that can detect weak magnetic fields, is essential for the realization the next Generation of high-density magnetic recording devices. Instead of that until now often used induction reading heads in the most recent Time heads used, which has the magnetoresistance effect (MR effect) of a Metal or a metal alloy (MR heads). Thereby can high-density, magnetically recorded information can be read, what with an induction head is difficult.

The in such minds However, metals or alloys used can obviously not used to read magnetic recordings with even higher density, because the size of her Magnetoresistance effect measured as resistance change rate only about 1%.

Thus, oxides with colloidal magnetoresistance, which have recently attracted attention because of their ability to provide a large magnetoresistance effect, have also been investigated for their usability in reading heads. For example, as reported on page 2041 of Physical Review Letters, vol. 77, the large magnetoresistance effect is seen in weak magnetic fields (10% or greater) observed at the grain boundary of a polycrystal L _1-x Sr _x MnO ₃ , a ferromagnetic perovskite , especially promising for use in highly sensitive magnetic sensors. A report published on page 8357 of Physical Review 8, vol. 54 describes an attempt to take advantage of the magnetoresistance effect of this perovskite as much as possible by making a so-called tunnel junction element consisting of an insulating layer comprising is arranged between two ferromagnetic layers. It is stated that a magnetoresistance effect of more than 80% has been achieved.

This Tunnel junction element but has the big one Disadvantage that it is difficult to produce. The reason is in that which is arranged between the ferromagnetic layers of the tunnel junction Insulating layer preferably not thicker than a few nanometers (nm) should be. The preparation of such a thin insulating layer, no shorts allows, is extremely difficult. Furthermore, the complexity of the element construction complicates the Manufacturing process and requires a complex process optimization. One can assume that these problems are diminishing Element size still pronounced will be. It is therefore considered very difficult to use the tunnel junction element for one Head for reading high density, magnetically recorded information too use.

on the other hand It is due to the recent breakthrough become possible in the oxide thin film breeding technology, high-quality, epitaxially grown oxide thin films to get that perfect crystal lattice match to the substrate exhibit. A report on page 1540 of Science, Vol. 266 For example, it indicates that even when it's on Reason for the crystallographic structure (crystal structure) of the substrate gives an atomic level difference (step) on the substrate surface, the thin film continues to grow, while the stepped state is maintained. Depending on the crystal structure the grown thin film and the layer growth conditions at this time are others Sections as those that are directly above the step, completely monocrystalline, while only the step section with a layer whose atomic arrangement is a disordered one periodicity has directions parallel to the surface of the thin are, more specifically, formed with a layer that has an antiphase domain boundary Has. However, the presence of an antiphase domain boundary is at In the field of compound semiconductors, it is undesirable because they provide carrier scattering and interface levels caused.

It An object of the invention is a magnetoresistance effect element indicate that a high magnetic sensitivity of at least 50% has, is easy to make and is effectively used as a magnetic sensor can be detected, the weak magnetic fields.

According to the invention there is provided a magnetoresistance effect element comprising an oxide substrate, that on its surface Atomic layer stages and on the substrate an epitaxially grown, has ferromagnetic oxide thin film, wherein the thin film formed on the atomic layer stages has an antiphase domain boundary Has.

According to one aspect of the invention, the ferromagnetic oxide thin film is represented by the formula RE _3-x AE _x Mn ₂ O ₇ wherein RE is at least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu , Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, AE is at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba, X is 0-3 and the oxide substrate is a <100> substrate made of SrTiO ₃ .

According to another aspect of the invention, the ferromagnetic oxide thin film is represented by the formula AE _2-x RE _x FeMO ₆ wherein RE is at least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, AE is at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba, M is Mo or Re, X is 0-2 and the oxide substrate is a <111> SrTiO ₃ substrate.

If a ferromagnetic oxide thin film is grown epitaxially on an oxide substrate that is on its surface Atomic layer stages has, as described above, forms a Anti phase domain boundary in the thin film directly above the substrate stages, and it leaves a large magnetoresistance effect observe when the electrical resistance in the direction perpendicular to the antiphase domain boundary is measured.

When a <100> substrate of SrTiO _{3 is used} as the oxide substrate, the effect of the invention is maximized by performing a chemical surface treatment which defines the atomic layer at the outermost surface of the substrate as TiO ₂ . When a <111> substrate of SrTiO _{3 is used} as the oxide substrate, a good effect is obtained if, prior to forming the layer of AE _2-x RE _x FeMO _6, a thin film of SrFeO ₃ terminates with a FeO ₂ surface , is formed as a buffer.

preferred embodiments The invention will now be described purely by way of example with reference to the accompanying drawings Drawings in which:

1 Figure 3 is a perspective view conceptually showing a portion of an inventive element near its antiphase domain boundary;

2 Fig. 12 is a plan view schematically showing a four-terminal resistance element which is an example of a magnetic sensor according to the present invention;

3 Fig. ₄ is a graph illustrating how the electrical resistance of a magnetic sensor according to the invention using Sr ₂ FeMoO ₆ varies as a function of applied magnetic field strength (10e = 10 ^-4 T);

4 an atomic force microscope image of the surface of a SrTiO ₃ substrate used in an example of the present invention;

5 Fig. 12 is a plan view schematically showing a four-terminal resistance element for measuring magnetoresistance anisotropy (a kind of magnetic sensor) used in the fourth example of the present invention;

6 Fig. 10 is a graph indicating an example of how the resistivity of the magnetic sensor used in the fourth example of the present invention varies as a function of the magnetic field intensity.

The Inventors have on an oxide substrate that atomic layer on its surface has, a ferromagnetic oxide thin film bred to so in the thin film an antiphase domain boundary directly above to form the substrate stages. When measuring the electrical resistance in the direction perpendicular to the formed boundary, the inventors have a big Magnetoresistance effect discovered. The present invention received one based on this discovery.

The inventors have studied combinations of ferromagnetic oxide materials and oxide substrates capable of producing the above-mentioned magnetic effect. It has been found that when the ferromagnetic oxide material used is represented by the formula: RE _3-x AE _x Mn ₂ O ₇ , wherein RE is at least one rare earth element (at least one of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), AE is at least one alkaline earth metal (at least one from the group Mg, Ca, Sr and Ba), and X is in the range of 0 to 3,
a <100> SrTiO ₃ substrate may be used as the oxide substrate having atomic layer steps on its surface.

Further, it has been found that when the ferromagnetic oxide material used is represented by the formula: AE _2-x RE _x FeMO ₆ , wherein RE is at least one rare earth element (at least one of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu), AE is at least one alkaline earth metal (at least one from the group Mg, Ca, Sr and Ba), M is Mo or Re and X is in the range of 0 to 2,
a <111> substrate of SrTiO ₃ can be used as the oxide substrate having atomic layer steps on its surface.

The following is an example of the use of Sr ₂ FeMoO ₆ (ie AE _2-x RE _x FeMO ₆ wherein AE = Sr, M = Mo, X = 0) as a ferromagnetic oxide material in combination with a <111> substrate of SrTiO ₃ as an oxide substrate having atomic layer steps on its surface.

1 Figure 11 is a schematic view of the environment in which one can observe an antiphase domain boundary in which Sr ₂ FeMoO ₆ . octahedron 3a consist of Fe ₆ and have iron atoms 4 depicted as large black spheres in their center. octahedron 3b consist of MoO ₆ and have molybdenum atoms 5 depicted as small black spheres in their center. In the ideal crystal structure are the octahedra 3a , the iron atoms 4 in their midst, and the octahedron 3b , the molybdenum atoms 5 in their midst, arranged alternately in three-dimensional space. However, this regular atomic arrangement is interrupted by the gray circles at the step portion 2 of the substrate 1 are indicated on which the octahedron 3b with the molybdenum atoms 5 lie next to each other. The height of the step is equal to the length of the lattice unit cell of the crystal.

As in 1 4, the arrangement of iron atoms and molybdenum atoms of the Sr ₂ FeMoO ₆ thin film epitaxially grown on the <111> surface of SrTiO ₃ shifts at the portion just above the substrate stage 2 , In particular, the (Fe-O-Mo-O) chain of the ideal crystal structure breaks down across the interface to form an antiphase domain boundary with the arrangement Fe-O-Fe or Mo-O-Mo. The reason for this is that in the Sr ₂ FeMoO ₆ composed of Fe-only and Mo-only layers stacked alternately in the <111> direction, the distance between the surfaces of the layers , which contain the same atoms, is about 0.46 nm, while the height of the step of the SrTiO ₃ substrate is half of this distance, ie, about 0.23 nm. As in 2 As shown, this thin film is photolithographically processed to form electrodes 11 and 14 to form the current at opposite ends of the thin film, wherein the antiphase domain boundary 15 placed between them, and around electrodes 12 and 13 to measure the electrical resistance in the middle of the thin film, with the antiphase domain boundary 15 between them, whereby a resistance measurement structure is formed, which makes it possible to measure the electrical resistivity, when the direction of the current is perpendicular to the substrate stage.

Sr ₂ FeMoO ₆ is a ferromagnetic substance whose Fe spins all have the same orientation in the ideal crystal. In the thin film of this example, however, the above-mentioned discontinuous arrangement of the iron atoms and molybdenum atoms causes the magnetization direction to be reversed on opposite sides of the interface. Since the conduction electron spin in this ferromagnetic material has exceptionally strong polarization (substantially 100% at low temperatures near that of liquid helium, 60-70% at 300 K), the electrical resistance of the interface in this state is maximum. The directions of magnetization on the opposite sides of the interface can be equalized by applying a magnetic field of several tenths Gauss to the device. The electrical resistance at the interface is reduced to a minimum when the magnetization direction is exactly the same on both sides. By optimizing the film formation conditions, this resistance change rate can be increased to over 50% under a magnetic field of 100 Gauss (1 Gauss = 10 ^-4 T) or less.

The above-mentioned magnetoresistance effect can also be obtained with an element using RE _3-x AE _x Mn ₂ O ₇ as the ferromagnetic oxide material and a <100> substrate of SrTiO ₃ as the oxide substrate.

When next will be examples of A method for producing an oxide substrate described on its surface Atomic layer stages has.

By annealing a substrate cut in the <111> direction for 2 hours at about 1000 ° C in a stream of Ar gas, ₃ stages having a height equal to that of SrTiO ₃ can be formed on the <111> surface Length of the lattice unit cell of the crystal (0.4 nm) is.

On the <100> surface of SrTiO ₃ , atomic layer steps can be formed by heat-treating a substrate cut in the <100> direction for 10 minutes at 800 ° C in an oxygen atmosphere of 1 mTorr (1 Torr = 133.322 Pa).

The <111> substrate of SrTiO ₃ formed with steps as described above is preferably superposed with SrFeO ₃ or SrMoO ₃ before the ferromagnetic oxide thin film is formed. This ensures that at the beginning of the formation of the Sr ₂ FeMoO ₆ layer, the first layer to be adhered is the one that does not consist of the previously attached atom, and ensures that an antiphase domain boundary is formed at each step portion.

In the formation of steps on the <100> SrTiO ₃ surface, the outermost surface assumes a complex configuration. By performing a chemical surface treatment at the outermost of the atomic layer To define the surface of the substrate as TiO ₂ , one can obtain a substrate which is formed only with steps whose height is equal to the length of the lattice unit cell of the crystal.

molecular beam epitaxy, Pulsed laser coating or any other film formation process, that a thin film can form, which is flat at the atomic level, as a method for forming the ferromagnetic oxide thin film on the oxide substrate be used whose surface with is formed the atomic layer stages.

The Magnetoresistance effect element according to the present invention can be made by a simple process that only a single one Step for thin film formation includes and has a high magnetic sensitivity of 50% or achieved more. It can therefore be effective for detecting weak ones Magnetic fields are used. Due to its high magnetic Sensitivity may be the magnetoresistance effect element according to the present invention Invention effective as a magnetic sensor for detecting weak magnetic fields be used. The element can be done in extremely simple processing steps be prepared and is therefore suitable for mass production and can be industrially produced with high productivity.

Now Examples of the invention will be described. However, the invention is not limited to the examples described.

example 1

An SrTiO ₃ substrate cut in the <111> direction was annealed for 2 hours at 1000 ° C in a stream of Ar gas to obtain a substrate having atomic layer steps parallel to the surface thereof, showing the slight deviation of the substrate cut surface from the <111> direction.

By laser ablation, a thin film of SrFeO ₃ having a thickness of 40 Å (1 Å = 10 ^-10 m) was formed on the substrate. This thickness corresponds to 10 SrFeO ₃ crystal unit cell periods.

The laser ablation target was a 20 mm diameter, 5 mm thick bead formed of SrFeO ₃ oxide polycrystal. The target and the substrate were placed opposite each other in a vacuum chamber, and the target was irradiated with a collimated beam of pulsed KrF excimer laser to grow a thin film of SrFeO ₃ as a buffer on the substrate.

At this time, the temperature of the substrate was 900 ° C and the oxygen partial pressure in the chamber was 1 × 10 ^-6 Torr. The energy density of the beam of the excimer laser at the target surface was 1000 mJ / cm ² per pulse and the pulse cycle period was 5 Hz.

The SrFeO ₃ target was then replaced by a Sr ₂ FeMoO ₆ target and a thin layer grown in a similar manner, the growth conditions being: substrate temperature 930 ° C, oxygen partial pressure 1 × 10 ^-6 Torr, laser power 1000 mJ / cm ² per pulse and a pulse cycle period of 5 Hz. The thickness of the Sr ₂ FeMoO ₆ layer was about 500 Å. The resulting film was processed by ordinary photolithography into a four-terminal resistance measuring element as shown in FIG 2 is shown. The element thus produced had a thickness of approximately 20 μm. The distance between the electrodes 11 and 14 was about 50 microns. The element was structured so that the direction of current flow (( 11 ) - ( 14 ) in the drawing) perpendicular to the direction of the step edge on the SrTiO ₃ substrate (( 12 ) - ( 13 ) in the drawing).

The magnetoresistance effect of the element was evaluated. The element was placed in an electromagnet and the intensity of the magnetic field in the electromagnet varied while a current of 10 μA between the electrodes 11 and 14 was designed so that it is perpendicular to the antiphase domain boundary 15 ran. The change in the electrical resistance of the element due to the change in the magnetic field intensity became due to the change in between the electrodes 12 and 13 calculated voltage. The magnetoresistance determined at 27 ° C is in 3 shown.

Of the specific electrical resistance of the element was maximum than no magnetic field was applied. Once a magnetic field has been applied, The specific electrical resistance decreased with increasing magnetic field intensity until it amounts to about 50% of the maximum value at a field intensity of 100 Gauss sank.

Example 2

A thin film of SrFeO ₃ was formed by surface processing as in Example 1 as a buffer on a <111> substrate of SrTiO ₃ provided with atomic layer steps.

The SrFeO ₃ target was then replaced by a sintered composite of Sr ₂ FeReO ₆ , and a thin film of Sr ₂ FeReO ₆ was deposited at a thickness of 500 Å, the conditions being: substrate temperature 850 ° C, partial pressure of oxygen 1 × 10 ^-6 Torr, energy density of the laser beam of the excimer laser 1000 mJ / cm ² per pulse and a pulse cycle period of 5 Hz.

One Resistivity measuring element with four terminals was according to the Example 1 prepared and measured the magnetoresistance effect at 27 ° C. The decrease in resistance was 60% at 100 Gauss.

Example 3

A thin film of SrFeO ₃ was formed by surface processing as in Example 1 as a buffer on a <111> substrate of SrTiO ₃ provided with atomic layer steps.

The SrFeO ₃ target was then replaced with a sintered composite of Sr _1.8 La _0.2 FeMoO ₆ , and a thin film of the same composition was deposited at a thickness of 500 Å, the conditions being: substrate temperature 930 ° C, partial pressure of oxygen 1 × 10 ^-6 Torr, energy density of the laser beam of the excimer laser 1000 mJ / cm ² per pulse and a pulse cycle period of 5 Hz.

One Resistivity measuring element with four terminals was according to the Example 1 prepared and measured the magnetoresistance effect at 27 ° C. The decrease in resistance was 55% at 100 Gauss.

Example 4

An SrTiO ₃ substrate cut in the <100> direction was etched with a mixed solution of NH ₄ -HF having a pH of 4.2, placed in a vacuum chamber and kept at 800 ° C. for 10 minutes in an oxygen atmosphere of 1 mTorr heat treated to coat the entire atomic layer on the outermost surface with a TiO ₂ surface to obtain a substrate having on its surface parallel atomic layer steps reflecting the slight deviation of the substrate intersecting surface from the <110> direction. An image of the surface of the substrate taken with an atomic force microscope is shown in FIG 4 shown. Out 4 It can be seen that the direction of the step edge was inclined by about 30 degrees and the step interval was about 60 nm. The step interval is determined by the substrate angle of inclination (English: substrate OFF angle) and can be arbitrarily regulated. Since the magnetoresistance is generated at the step position, the magnitude of the magnetoresistance can be regulated by regulating the step interval.

Laser ablation formed a thin film of La _1.2 Sr _1.8 Mn ₂ O ₇ with a thickness of 100 Å on the substrate. This thickness corresponds to 10 La _1.2 Sr _1.8 Mn ₂ O ₇ crystal unit cell periods.

The laser ablation target was a 20 mm diameter, 5 mm thick bead formed from an oxide polycrystal of La _1.2 Sr _1.8 Mn ₂ O ₇ . The target and the substrate were placed opposite each other in a vacuum chamber, and the target was irradiated with a beam of a pulsed KrF excimer laser to grow a thin film of La _1.2 Sr _1.8 Mn ₂ O ₇ on the substrate. At this time, the temperature of the substrate was 970 ° C and the oxygen pressure in the chamber was 100 mTorr. The energy density of the beam of the excimer laser at the target surface was 2000 mJ / cm ² per pulse and the pulse cycle period was 10 Hz.

The resulting film was processed by ordinary photolithography into a four-terminal resistance measuring element as shown in FIG 5 is shown. The element was structured so that the direction of current flow perpendicular to the direction of the step edge 29 on the SrTiO ₃ substrate was. In particular, the direction of the step edge after film formation was first confirmed with an Atomic Force Microscope (AFM). Thereafter, photoresist patterning was performed so that the direction of the step edge is one direction (FIG. 21 - 26 ) and the direction that runs on both sides of the step edge, one direction ( 24 - 27 ) was. The layer could simply be etched with hydrochloric acid or aqua regia. The photoresist was then dissolved and removed with acetone to complete the fabrication of the element. The reference number 29 in 5 denotes the antiphase domain boundary. The magnetoresistance effect of the element was evaluated. The element was placed in an electromagnet and the intensity of the magnetic field in the electromagnet varied while a current between the electrodes 22 and 25 was created. The change in the electrical resistance of the element due to the change in the apparent field intensity became due to the change in between the electrodes 23 and 28 calculated voltage. The magnetoresistance determined at -200 ° C is in 6 shown. The specific electrical resistance of the element was maximally applied as no magnetic field. Once a magnetic field was applied, the resistivity decreased with increasing magnetic field intensity until it dropped to about 30% of the maximum value at a field intensity of 100 Gauss.

Claims (5)

Magnetoresistive effect element comprising an oxide substrate ( 1 ), which on its surface atomic layer stages ( 2 and an epitaxially grown ferromagnetic oxide thin film on the substrate, the thin film formed on the atomic layer stages having an antiphase domain boundary. A magnetoresistance effect element according to claim 1, wherein the ferromagnetic oxide thin film is represented by the formula RE _3-x AE _x Mn ₂ O ₇ , wherein RE is at least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm , Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, AE is at least one alkaline earth metal selected from the group consisting of Mg, Ca, Sr and Ba, and X is 0-3 and the oxide substrate is a <100> SrTiO ₃ substrate. A magnetoresistance effect element according to claim 1, wherein the ferromagnetic oxide thin film is represented by the formula AE _2-x RE _x FeMO ₆ , wherein RE is at least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu Is selected from the group consisting of Mg, Ca, Sr and Ba, 2 and the oxide substrate is a <111> SrTiO ₃ substrate. A magnetoresistance effect element according to claim 2, wherein the surface of the <100> substrate of SrTiO _{3 is} subjected to a chemical surface treatment to make it a TiO ₂ surface. A magnetoresistance effect element according to claim 3, wherein a thin film of SrFeO _{3 is} disposed on the surface of said <111> substrate.